1. Field of the Present Invention
Apparatuses and methods consistent with the present invention relate to a fiber pulse laser apparatus, and more particularly, to a method of controlling pulse outputs of the fiber pulse laser apparatus such that a first pulse output is equalized in magnitude with second and subsequent pulse outputs in a pulse laser that oscillates pulses through a combination of a master oscillator and an optical amplifier (hereinafter, referred to as an MO-PA type laser apparatus), and a fiber pulse laser apparatus that controls a pulse output according to the control method.
2. Description of Related Art
In the related art, for example, MO-PA type laser apparatuses are disclosed in various documents.
Among these disclosures, Japanese Patent No. 2658351 discloses a technique for controlling a strength ratio of a peak value of a first pulse to each of peak values of second and subsequent pulses for wafer marking.
Japanese Unexamined Patent Application, First Publication No. H7-74422 discloses a technique for monitoring a population inversion state of an oscillator and oscillating pulses, with a low Q value of only a first pulse, based on the monitored population inversion state.
Japanese Patent No. 3411852 discloses a technique for operating an excitation light source into an idle state to keep the magnitude of a first pulse constant.
Japanese Patent No. 3364171 discloses a technique for slowing a marking speed accordingly to match with a smaller first pulse to make printed characters uniform.
Japanese Unexamined Patent Application, First Publication No. 2004-337970 discloses a technique for shortening a rising time by increasing the current of an excitation light source at the start-up of the light source.
In MO-PA type laser apparatuses, a laser output depends generally on an output of an excitation light source, such as a laser diode (LD) of a power amplifier (PA) unit (hereinafter referred to as a pump LD). If an output of the pump LD is zero, the laser output is zero even though the master oscillator (MO) unit oscillates pulses. In addition, when a trigger signal is input to a Q switch of the MO unit, Q switch pulses are generated in synchronization with the trigger signal.
In general, MO-PA type laser apparatuses have a disadvantage in that outputs of first several pulses become small immediately after the laser is started with pulse operation. On the contrary, other types of laser oscillators that do not employ MO-PA type have a different disadvantage in that only the first pulse is increased.
The present invention addresses a disadvantage relating to an output of a first pulse in an MO-PA type laser apparatus. The cause of the disadvantage of the first pulse in the MO-PA type laser apparatus is a slow start-up time of the PA unit. For example, although an interval between a pulse and a next pulse operated at 20 kHz is 50 μs, it takes between 200 microseconds and 500 microseconds until an amplifier reaches a completely stable operation at start-up. During this time, pulses become small in energy and peak value.
In addition, although the MO unit can start slightly earlier than the PA unit, if the start-up time is shortened, the start-up time of the MO unit may cause disadvantages in that the start-up time of the MO unit may present a bottleneck, thereby making it difficult to obtain any advantages from a reduction in the start-up time.
In the related art, an operation control at start-up of a pump LD is directed to reduce a delay time which may occur when the pump LD supplies excited light (see Japanese Patent No. 3364171 and Japanese Patent Application, First Publication No. 2004-337970), which is also an object of the present invention. This related-art technique cannot provide a solution to the essential problem that it takes a long time for the LD to produce a desired output and stabilize a population inversion of an amplification medium, thus giving no advantages with respect to the following points:                To make the pulse peak value constant from “first pulse” under all operation conditions.        To reduce the start-up time of the MO unit.        
In addition, the advantages of the above related-art technique are inferior to the advantages of the present invention regarding minimization of the time until an output is stabilized.